/Engine/Plugins/Media/PixelStreaming/Source/PixelStreaming/Public/IPixelStreamingStreamer.h
Set the target screen rectangle for this streamer. This is used to when the streamer doesn't have a singular target window / viewport and as such we just use the manual scale.
void SetTargetScreenRect ( [TWeakPtr](API\Runtime\Core\Templates\TWeakPtr)< FIntRect > InTargetScreenRect )